原来一直觉得ajax的defer方式已经是多余，现在才觉得asyn：false设置成同步方式都是有用的。打个比方，在ready页面加载又要保存切换选项卡状态又要保存前一搜索结果的话，就有用。

          $.ajax(
        {
            type: "post",url: "./HelpCenterTabSwitch.ashx",data: "type=6&flag=1&tid=" + encodeURI(encodeURI(PTid)),cache: false,<span style="color:#ff0000;"> async: false,</span>
            dataType: "text",success: function (msg) {
<span style="background-color: rgb(204,102,204);">
                $("#selection").show();
                $("#UlContent li").remove();
                $("#UlContent").append(msg);

</span>
            }
        });
            }
            if (window.localStorage.getItem("keyword") == "description" && typeof (flag) != "undefined") {
                $("#problem").removeClass("at");
                $("#description").addClass("at");
                $.ajax(
       {
           type: "post",data: "type=4&flag=1&tid=" + encodeURI(encodeURI(PTid)),<span style="color:#ff0000;">  async: false,</span>
           dataType: "text",success: function (msg) {

           <span style="color:#ffff00;">  </span><span style="color:#cc33cc;">  $("#selection").show();
               $("#UlContent li").remove();
               $("#UlContent").append(msg);</span>


           }
       });


            }
            if (window.sessionStorage.getItem("keyword2") != null&&window.sessionStorage.getItem("keyword2").replace(/(^\s*)|(\s*$)/g,"") != "" && window.sessionStorage.getItem("keyword2") != "请输入关键字搜索")
            {
             
             
                //$.ajax({
                //    type: "POST",//    anync: false,//    url: "HelpCenterSuggestion.ashx",//    cache: false,//    dataType: "text",//    data: { m: window.sessionStorage.getItem("keyword2") },//    success: function (result) {
           

                        $("#UlContent li").remove();
                        $("#UlContent li").removeAttr("padding");
                       
                            $("#SearchResult").html("");
                            $("#SearchResult").html("搜索结果");
                //$("#UlContent").append(result);
                            $("#UlContent").append(window.sessionStorage.getItem("searchResult2"));
                            $("#SearchResult").css("margin-top","");
                            $("#SearchResult").css("margin-bottom","");
                            $("#SearchResult").css("text-align","");
                            $("#SearchResult").css("border-bottom","1px solid #e2e3e7");
                            
                            $("#selection").hide();
                            $("#content").show();
                       
                      
                //    }


                //});
            }

这边如果不设置为asyn为false的话，当执行前两段后的返回搜索结果最后还是会异步执行上面这段：

<span style="background-color: rgb(204,204);">      $("#selection").show();
                $("#UlContent li").remove();
                $("#UlContent").append(msg);
</span>